The invention relates to a gear device.
Gear devices of this type are generally configured as planetary gears (for example Johannes Looman “Principles, Constructions, Applications in Vehicles”, 3rd edition, volume 26). In their simplest constructional form, planetary gears of this type have a first path in the form of the external circumference of a sun wheel, a second path in the form of the internal casing of a ring gear which surrounds the sun wheel and at least one planet wheel which is disposed between these paths and mounted rotatably on a planet carrier (web). The planet wheel is in operational connection at its circumference both with the sun wheel and with the ring gear, by which there should be understood here for example a meshing (toothed gearing) or a rolling assembly (friction gear).
The actuation or power take-off in planetary gears of this type is effected for example in that either in the case of a securely-retained sun wheel, the ring gear is driven, or in the case of a securely-retained ring gear, the sun wheel is driven and the rotational movement which is consequently transmitted by the planet wheel to the planet carrier is used. Conversely however, also the planet carrier can be driven and the consequently produced rotational movement can be transmitted to the sun wheel or ring gear.
The power transmission in the region of the carrier is effected, independently of whether the latter is used as actuation or power take-off element of the gear, via the bearing axle which is situated in the centre of the planet wheel, about which the planet wheel is mounted rotatably on the carrier. Bearing axle and power transmission axle hence coincide.
Deviating therefrom, it is known in the case of crank gears, to dispose a sun wheel and a planet wheel which is in operational connection with the latter on a crank disc, and to provide the planet wheel with a power transmission axle which is disposed eccentrically relative to its bearing axle and is coupled to the one end of a connecting rod (PCT-WO 88/08095). In practice, a serious problem resides thereby in the fact that the power transmission axle does not follow a circular orbit because of the inherent rotation of the planet wheel effected during rotation about the sun wheel, but instead a complicated generally cycloid-type trajectory. This trajectory can indeed be approximated to an elliptical path by optimisation of the sun and planet wheel diameters. However, achievement of a circular orbit which is desired per se is not possible in the case of gears of this type. It would be equally impossible to achieve for example a linear movement path of the power transmission axle in the case where the paths which are disposed on both sides of the planet wheel concern linear paths.
In the case of gears of this type, a circular orbit for the power transmission axle has therefore only been able to be achieved to date when the latter coincides with the bearing axle of the planet wheel, which coincides simultaneously also with the rotational axle of the planet wheel. This has the result that a force exerted upon the power transmission axle is apportioned respectively half to the operational connection between the sun wheel and the planet wheel and to the operational connection between the planet wheel and the ring gear and thus only half can be transmitted to the sun wheel or ring gear and hence be made useful. In addition, the path which is transmitted to the ring gear during a revolution of the planet wheel about the central axle of the planetary gear is always twice as large as the path which the bearing-or power transmission axle of the planet wheel thereby describes about the central axle of the planetary gear. Therefore, during power input or power output at the bearing axle, the result is halving of the forces with doubling of the path covered or vice versa. In other words, of a force exerted upon the power transmission axle, only half is transmitted to the ring gear, which thereby covers twice the path of the power transmitting axle.
These conditions are unalterable with the construction of planetary gears and comparable gears. Numerous inconveniences for practical application arise therefrom, in particular also with respect to the transmissible rotational moments and the possible transmission ratios.